1. Field of the Invention
The present invention relates to a frequency signal enabling apparatus and the method thereof, and more particularly, to a frequency signal enabling apparatus and the method capable of filtering noise and fast enabling the digital IC when transferred from a power-saving mode into an operating mode.
2. Description of Related Art
Due to the current trend of electronic product for lighter, slimmer and portability, how to enhance the power-saving function has become the development focus for various manufacturers. The conventional power-saving function turns off the input frequency signal (XTAL) of the microprocessor after the microprocessor enters a power-saving mode from an operating mode; and while the microprocessor returns to the operating mode from the power-saving mode, the input frequency signal is turned on. While the input frequency signal was turned on from off, the aforementioned power-saving function will generate a transient noise signal. The microprocessor must wait a period of time to proceed with operating until the input frequency signal became stable. Otherwise, if the microprocessor begins to operate while the input frequency signal was not yet stable, it is easy to crash or calculate with the wrong results.
A conventional manner for solving aforementioned problem uses a counter circuit. First, the circuit designer sets a safe count value that when the counter counts from zero to the said count value, it means the input frequency signal is stable, then the microprocessor is enabled to proceed with operating.
The drawback of the conventional manner is that a large chip area is wasted. Especially for some light, slim electronic products, the chip with too large area is against the design rule. Thus, for the industry, it is necessary to provide an effective solution to avoid producing an error operation while the microprocessor or other digital IC returns the operating mode from the power-saving mode.